<html>

<head>
    <script src="https://unpkg.com/vue"></script>

    <div id="app">
        <p>{{ message }}</p>
        <p v-if="seen">现在你看到我了</p>
        <p v-if="seen2">现在你看不到到我了</p>
    </div>

</head>

<body>
    <script>
        var app = new Vue({
            el: '#app',
            data: {
                message: 'Hello Vue.js!',
                seen: true,
                seen2: true,
            }
        });
    </script>
</body>

</html>